Measurement of thermal effects of diode-pumped solid-state laser by using digital holography

Thermal lensing is one of the most important factors that can affect the performance of high-power solid-state lasers, such as limiting the power scaling capability and deteriorating output beam quality. In this paper, a novel and accurate measurement of digital holography is proposed to determine the thermal lensing of diode-pumped solid-state lasers with high resolution. The digitally recorded hologram can reveal the phase change when light travels through the laser gain medium. From the phase map, we can obtain the index variations induced by temperature differences inside the laser crystal when it is pumped by laser diodes, as well as determine the focal length of the integrated thermal lensing focus length. There was much work on measuring the static laser medium thermal lens because there is no laser output from the cavity in the setup. Our experiment setup was able to achieve online measurement with laser output at the same time. The measuring result can provide an accurate guide for compensating the thermal lensing in laser design to achieve high-power output and good beam quality. Moreover, detailed index variations in the direction of the laser crystal cross-section can be numerically reconstructed, by which the thermal effects, pump uniformity, crystal uniformity, etc., can be revealed from the holography result.